There is a case where a wide area needs to be monitored by using a sensor. For example, a search of a rescuee in an area where a disaster has occurred, a rescue support, monitoring of important facilities and so on are considered.
When a target as a monitoring object moves in a monitoring area at a comparatively high speed, radar can become effective as a sensor monitoring the target to detect in a short period corresponding to a moving speed of the target. In such a case, a technique is known that estimates a position of the target by approximating the motion of the target between continuous detections to a uniform linear motion.
Oppositely, when the target moves in a wide monitoring area at a comparatively low speed, the trajectory of the motion of the target becomes complicated so that there is a possibility that it becomes more difficult to predict the position of the target. Moreover, when the monitoring area is wider than the detection range of the radar, an aircraft and an artificial satellite having the radar need to be moved to a location near the target.
In conjunction with the above description, Patent Literature 1 discloses a technique of identity determining means. This identity determining means is characterized by acquiring the following elements to determine the target identity from target data obtained as a target observation result. This identical target determining apparatus includes probability density function expression means, transition probability calculating means, distance calculating means and the identity determining means. At this time, the probability density function expression means shows a spatial existence of the observed target as a probability density function. The transition probability calculating means adjusts to time, the probability density functions of both of a previously observed target and a twice previously observed target, by using a transition probability. The distance calculating means calculates a distance between reference positions of the probability density functions which are adjusted to time. The identity determining means determines the target identity based on the distance between the reference positions.
Also, Patent Literature 2 discloses a sensor integration system. This sensor integration system includes a processor, a storage unit connected with the processor, and an output unit connected with the processor. At this time, the storage unit holds observation data observed by a plurality of sensors. The observation data contain data of a first kind and data of a second kind. The observation data of the first kind contain coordinate values of one or more targets and times when the coordinate values are observed. The observation data of the second kind contain data showing the outwards of one or more targets, times when the data showing the outwards are observed, and coordinate values of the one or more targets. The storage unit further holds data showing a certainty of each coordinate value. The processor estimates movement trajectories of the one or more targets based on the coordinate values of the one or more targets which are contained in the observation data of the first kind, the data showing the outward form of the one or more targets which are contained in the observation data of the second kind, and the observation data of the second kind. The processor predicts the coordinate value of each target at a first time based on the movement trajectory at a time previous to the first time. The processor specifies the most likelihood coordinate value of each target at the first time by calculating an average with weights based on the certainty or a center of gravity, based on the observation data, in which a distance to the predicted coordinate value is within a predetermined value, of the coordinate values contained in the observation data at the first time. The processor corrects the movement trajectory estimated to contain the specified coordinate value. The output unit outputs data showing the movement trajectory.